The present invention relates to the detection of sources of p-static interference. More particularly, the invention relates to a method and apparatus for detecting p-static interference caused by inadequate electrical bonds between components of an aircraft.
P-static (or "Precipitation" static) is a result of triboelectric charging of an isolated body. Triboelectric charging is a phenomenon that produces static electricity by friction. The charge transfer may take place, for example, when particles (rain, ice, dust, sand, etc.) impinge an isolated surface and charge the surface to a higher potential than the surrounding area. The phenomenon is often seen on aircraft when rain or ice impinge the aircraft and leave an overall negative charge on the aircraft. If unaccounted for, the charge on the aircraft often reaches an electrical potential at which the aircraft discharges to the atmosphere by corona, sparking, or streamering. The charge build-up may also cause sparking between inadequately electrically bonded components of the plane. This corona, sparking, and streamering causes radio frequency interference which can degrade the operation of electrical and radio equipment onboard the aircraft. This radio frequency interference noise is typically referred to as precipitation static or p-static.
P-static interference is typically controlled through the use of static dischargers and proper electrical bonding. Static dischargers slowly disperse excess charge on an aircraft back to the atmosphere without creating corona, sparking, or streamering. Further, proper electrical bonding ensures that the aircraft components that are exposed to triboelectric charging are at a common voltage potential relative to each other so that differential voltages are not created between inadequately bonded components.
When p-static interference occurs in an aircraft, it is important that the source of the static be located. Prior apparatus and methods for locating the source of p-static interference have included the use of high voltage (approximately 70,000 volts DC) test sets that flood an aircraft with highly charged ions. During application of this voltage, the radio receiver on the aircraft is monitored for the appearance of interference.
These methods and apparatus, however, suffer from a number of disadvantages. First, these test systems use dangerous voltage levels that can injure a test operator if proper procedures are not followed. Second, the test apparatus is typically large, bulky, and expensive, thereby limiting its widespread use. Third, the test results have been known to be susceptible to false detection of inadequate bonds as possible sources of p-static interference.
Accordingly, a need has arisen for a p-static source locator that is less susceptible to false readings. It is also desirable that the locator be less expensive, and that it operate at lower voltages. The present invention not only addresses these needs, but also provides a system that is more compact and easier to use than existing systems.